BARNSTABLE, Mass. — He is hailed as the second-coming of Scott Brown: A young, telegenic military man with moderate Republican views and a candidate with a real possibility of winning the Massachusetts Senate seat.

But Gabriel Gomez is quick to warn that this is not 2010. And on this point, he agrees with Democrats: He’s no Scott Brown.

“This is a different election, I have a different opponent, it’s a different time,” Gomez said in an interview this week at a Cape Cod diner.

Despite some early polls showing a tight race between Gomez and liberal Democratic Rep. Ed Markey, the hurdles facing the Republican nominee are high. If he were to pull off a victory in next month’s special election to replace John Kerry, it would mark an even bigger upset than when Brown shocked the political world by winning Ted Kennedy’s seat in January 2010.

Unlike Brown, who barnstormed the state in a pickup truck and demonstrated skills as a savvy retail politician, Gomez is a true political neophyte untested in the media glare and unpolished on the stump. Gomez and Brown differ on several key issues, including over abortion and gun control, something Democrats are quick to point out.

And Gomez is already facing the full wrath of the national Democratic machine that was caught sleeping when Brown was first elected. Michelle Obama is scheduled to appear at a high-dollar fundraiser later this month and even President Barack Obama is expected to visit the state, a rarity for a Senate candidate these days.

A former private equity executive, Gomez poured plenty of his own cash into the Senate primary, something he’s not ruling out doing in the general election. But his own personal fortune and effective tax rate came under scrutiny Thursday after a story in The Boston Globe questioned a $280,000 tax break he may have inappropriately claimed on his 112-year-old South Shore home.

While Gomez insists he did nothing wrong, the revelations are giving Democrats new fodder to undercut the GOP candidate’sattempt to introduce himself as a “new kind of Republican.” And they are seeking to tie Gomez to another famous Republican from the state: Mitt Romney, who has his own past ties to private equity.

“We’ve seen this movie before in Massachusetts: A guy who says he’s a businessman because he looks good in a suit,” said John Walsh, chairman of the Massachusetts Democratic Party.

With the GOP primary win behind him, the next several days are a critical period for Gomez. He must prove his viability in the race by moving past the damaging Thursday story, withstand attacks from Democrats and narrow the deficit in the polls in a blue state — all in order to convince big GOP donors and outside groups that his candidacy is worth the investment. Indeed, a big question remains how much money national Democrats will pour into the contest to shore up Markey, and whether Republicans — and their outside allies — will decide to pitch in and aim to snatch the seat for their column, hoping to increase their Senate numbers.

Much of the race until Thursday had been dominated by Gomez’s refusal to sign a pact with Markey called the “People’s Pledge,” which then-candidate Elizabeth Warren and Brown agreed to in 2012 prevent outside groups from spending money in the state. That decision by Gomez could open the door to outside groups spending big bucks to push him over the finish line. But Republicans privately say Gomez needs to prove the investment is worth it.

“I don’t know the details of the strategy or the plan at this point,” said Sen. Jerry Moran, when asked if his National Republican Senatorial Committee would pump money into the race. “We believe he’s a great candidate and will be helpful in substantial ways.”

After several post-primary polls showed Gomez trailing Markey by single digits, a Suffolk University survey Wednesday put the Democrat up 17. The good news for Gomez: 32 percent of voters had barely heard of him and hadn’t yet formed an opinion.

So the race on both sides now is focused on one thing: Defining Gomez.

“Scott Brown was a known entity: He was someone who had a track record here in the state,” said Steve Middlebrook, a retired school administrator attending the Boston rally for Markey. “We’ll see what [Gomez is] like when people ask him tough question.”

The fight in Massachusetts is emblematic of races where the party in power attempts to nationalize the contest, while the minority party seeks to turn the race into a debate over personalities rather than ideology. That was on full display earlier this week in a House special election in a conservative South Carolina district, where Republican Mark Sanford won despite a scandal-tarred past. And in an interview, Markey argued that the race was a priority for the Democratic agenda.

It was a selling point before a packed room of young professionals at a stuffy Boston pub earlier this week.

“This election is a referendum on the second term of Barack Obama,” Markey declared, with Gov. Deval Patrick (D) standing beside him.

Just as Gomez is trying to introduce himself to voters, shaking hands outside Fenway Park and appearing in more remote areas, Markey and Democrats are trying to instill fear in their base that Gomez can win if they take him for granted.

In public appearances, the 47-year-old Gomez is quick to point out his compelling biography. A native Spanish speaker who was raised by Colombian immigrants, Gomez learned English in elementary school, earned his wings as a Navy pilot and later transferred to the elite Navy SEALS unit. After leaving the Navy in 1996 to earn an MBA at Harvard Business School, Gomez worked in the private equity industry, amassing a personal fortune estimated between $11.2 million and $44.8 million. He donated to Obama in the 2008 primary, but later voted for John McCain and Romney.

“I don’t know a lot about him, but he just seems like a stand-up kind of guy,” said Brian Smith, a 50-year-old owner of a grocery store here whose hand Gomez shook.

During a three-way GOP primary last week, Gomez spent more money on TV than his opponents, and lent his campaign $600,000 of his own cash. He won the primary in the aftermath of the Boston bombing, after he was extensively quoted by the local media because he ran the marathon, finishing in just over four hours as he was conducting interviews and shaking hands along the route.

With no political experience, Gomez is trying to paint a stark contrast to the 66-year-old Markey, who has served in the House since 1976, allowing the Republican to rail on “career politicians.”And he’s pitching himself as a “new kind of Republican,” something he hopes plays well with moderate Democrats and independents put off by Markey’s staunchly liberal views.

Gomez calls himself “pro-gay marriage” and says he’d vote to repeal the Defense of Marriage Act. He backs the Senate’s comprehensive immigration bill. And he says he would have bucked much of his party by endorsing the bill to expand background checks on commercial gun sales.

“Some stances and some beliefs I have that don’t always coincide with the majority of Republican Party,” he added. And while he spoke with Senate Minority Leader Mitch McConnell (R-Ky.) this week, he promised he wouldn’t “kowtow” to GOP leaders.

Still, there are some ways in which Gomez is like national Republicans. And he was forced to emphasize those points in the GOP primary, something Brown hardly had to worry about because he faced little challenge in his primary. Unlike Brown, Gomez opposes a ban on assault weapons; he opposes abortion rights and he raised concerns over the Dodd-Frank financial reform law that Brown supported.

Brown, who lost his 2012 reelection campaign to Elizabeth Warren, declined to be interviewed. But Gomez said he received political advice from Brown when the two ran the same 5-K race last month.

“His advice was basically: be yourself, be true and go out there and be consistent with what you’re saying,” Gomez said.

Some of that advice may have been to exhibit caution.

Gomez is reluctant to detail his views about some controversial issues. He refused to say whether he believes Obamacare should be repealed, only that he believed it wouldn’t be overturned by Congress.

While he said that lower tax preferences for “carried interest” should be “part of the discussion” as part of a larger Tax Code overhaul, he wouldn’t say whether private equity managers who benefit from the current law should be hit with higher taxes. Instead, he’s in line with his party on taxes: “I don’t think you need to raise taxes.”

And even though he backed a compromise background checks bill, during the primary, he opposed broader universal background checks on private and commercial gun sales. In the interview, he said he wanted to review legislation on the issue before staking out a position.

And while the issue has dominated political debate over the last two years, Gomez won’t take a position on the Medicare overhaul proposed by Rep. Paul Ryan (R-Wis.), saying he still has to review it.